1. Field of the Invention
The present invention relates to the technical field of fibre laser transmission and amplification, and specifically a high-efficiency parallel-beam laser optical fibre drawing method and an optical fibre.
2. Description of the Related Art
A fibre laser is essentially designed to convert low quality pump laser into higher quality laser output. As the application fields are constantly extending, the output power of the fibre laser needs to be risen unceasingly. Currently, a high power fibre laser and a fibre amplifier mainly use double-cladding doped optical fibres. Compared with the divergence angle of multimode pump beam emitted by a semiconductor pump laser, the double-cladding doped optical fibres have a rather small diameter of cladding. Therefore, how to efficiently couple pump light to the inner cladding of the double-cladding optical fibres is a core technology to obtain high power optical fibre laser output.
At present, pump coupling technology can be roughly divided into end pump coupling technology and side pump coupling technology. Regarding end pump coupling technology, a pump light is coupled to the inner cladding of a double-cladding optical fibre from one or two end faces of the double-cladding optical fibre. As for side pump coupling technology, a pump light is coupled to the inner cladding of a double-cladding optical fibre from the side of the double-cladding optical fibre. As the two ends of the optical fibre are not occupied, the pump light is distributed more uniformly in the optical fibre, thereby facilitating signal light input and output, fibre splicing and signal measurement etc. Typical side pump coupling technology includes V-groove method, embedded reflector method, angular polishing method, diffraction grating pump coupling and GTWave technology etc. In GTWave technology, by using the unique structure of a parallel-beam laser optical fibre drawn from combined active and passive optical fibre performs, a pump light is coupled to a gain optical fibre cable along an axial module of the optical fibre; when the outer diameter or numerical aperture of the optical fibre is comparatively low, a multimode pump light in the passive optical fibre can be efficiently coupled to the active optical fibre; and when the optical fibre is not damaged or deformed, multipoint segmented pumping along the length of the optical fibre can be achieved through pump light injection by discontinuously peeling the passive optical fibre, thereby preventing a problem that heat load is excessively high as a result of centralized incident power, and obtaining stable high power laser output from the gain optical fibre. As shown in FIG. 1, a structure diagram of a parallel-beam optical fibre, a gain optical fibre a1 containing a quartz component and at least one pump optical fibre a2 are arranged in parallel and are physically fused at a contact part; a low refractive index coating a3 covers the outer layer of the gain optical fibre a1 and the pump optical fibre a2; and a protective coating a4 covers the outermost layer. A fibre core all of the gain optical fibre a1 is doped with a rare earth element; when a pump light penetrates through the fibre core all, laser level “population inversion” will be triggered through the rare earth element, and a cladding of the gain optical fibre will form a resonant cavity to generate laser oscillation output. When injected from one end of the pump optical fibre a2 peeled from the parallel-beam laser optical fibre, the pump light will be coupled to the gain optical fibre a1 from the joint of the pump optical fibre a2 and the gain optical fibre a1, thereby greatly improving pump coupling efficiency, and preventing a problem of local heat management resulted from point contact in conventional side pumping.
A current making process of optical fibres similar to the parallel-beam optical fibre structure mainly uses a low speed parallel-beam drawing method, through which a gain optical fibre perform and at least one pump optical fibre perform are fixed on a optical fibre drawing tower in a certain arrangement pattern, and are concurrently stretched under certain speeds and tensions till two adjacent optical fibres are in contact, so that light can penetrate through adjacent optical fibres. Although the current single optical fibre drawing process is mature, concurrent drawing of multiple optical fibres needs to overcome some difficulties. For example, when multiple optical fibre performs are combined and drawn, as the drawing tension and temperature of each perform as well as the coating pressure against corresponding optical fibres are varied, effective control and adjustment are hard to be achieved. Besides, in the current perform combination drawing method, as multiple columnar performs are combined before drawing, and optical fibre performs are melted under low speed and high tension to ensure that optical fibres can be effectively fused, the quartz parts of the optical fibres drawn are melted and tightly combined and cannot be peeled as required, thus multipoint pump light injection along the length direction cannot be achieved. When the parallel-beam laser optical fibre is put into actual use, multiple points need to be selected along the length direction of the optical fibre to peel the pump optical fibre so as to achieve multipoint pumping along the length direction of the gain optical fibre as well as tight contact (or fusion) of the pump optical fibre and the gain optical fibre; and the key to achieve the application performance of the parallel-beam laser optical fibre is to achieve the peelability of the pump optical fibre.